Apparatus for pyrolytic decomposition of waste materials

ABSTRACT

A hearth apparatus for use in combination with a pyrolysis chamber for waste disposal adapted to support and provide conditions for efficient combustion, pyrolytic decomposition and ensuing removal of the resulting waste residue which comprises at least a pair of oppositely disposed elongated sloping refractory walls which are spaced by and terminate in an elongated openably closed bottom to form a trough-like structure, a plurality of tubes connected to a pressurized air supply passing through the sloping walls providing air sufficient to maintain proper combustion and to fluidize and move pulverulent residue down the sloping walls to a storage area or discharge.

United States Patent [1 Altmann Oct. 7, 1975 1 APPARATUS FOR PYROLYTIC'DECOMPOSITION OF WASTE MATERIALS [22] Filed: May 28, 1974 [21] Appl.No.: 473,349

[52] US. Cl. 110/8 R; l10/75 R; 110/165 R [51] Int. Cl. F23G 5/00; F23L1/00; F23] 1/00 [58] Field of Search 110/8 R, 18 R, 28 Q, 72 R,

Primary ExaminerKenneth W. Sprague Attorney, Agent, or Firm-Charles J.Speciale, Esq.

[5 7] ABSTRACT A hearth apparatus for use in combination with apyrolysis chamber for waste disposal adapted to support and provideconditions for efficient combustion, pyrolytic decomposition and ensuingremoval of the resulting waste residue which comprises at least a pairof oppositely disposed elongated sloping refractory walls which arespaced by and terminate in an elongated openably closed bottom to form atrough-like structure, a plurality of tubes connected to a pressurizedair supply passing through the sloping walls providing air sufficient tomaintain proper combustion and to fluidize and move pulverulent residuedown the sloping walls to a storage area or discharge.

4 Claims, 8 Drawing Figures APPARATUS FOR PYROLYTIC DECOMPOSITION OF'ASTE MATERIALS BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates generally to a pyrolytic waste disposal systemand more particularly to an improved hearth structure intended for usewith a pyrolysis chamber for waste combustion and pyrolysis and removalof residue therefrom.

2. Description of the Prior Art Thermal destruction of waste materialsin quantities of up to several tons an hour is commonly accomplished intwo classes of equipment, incineration and pyrolysis.

Current incineration equipment provides a waste receiving chamber whichis generally a refractory lined box having a door for the extrance ofwaste in one wall, an exit gas port in a second wall, a forced airburner in one or two other walls and a hearth, usually comprised ofmetal grates which support the waste. This hearth permits the waste,when decomposed enough to become friable, to fall into an ash pit. Theeffluent gas from this chamber is largely oxidized hydrocarbon althoughit contains some combustible components and unburned particles ofcombustible and inert matter which may be carried in the turbulent, highvelocity gas. Secondary chambers are usually provided to complete thecombustion but frequently do not accomplish this effectively. The ashwhich has fallen through the grate usually contains much unburnedmatter. This ash is usually removed, when the equipment has been shutdown by mechanical devices, either powered or manual. The items whichwill not fall through the grates must be removed, from time to time, inorder to achieve full use of the chamber. The grates may be ofstationary or moving type but all are subject to destructive conditionsdue to high temperatures, oxidizing conditions and mechanical abuse.Since this equipment frequently is inefficient and an environmentalpollutor, it is falling into disfavor.

Pyrolytic decomposition equipment, now becoming more common, meets theshortcomings of the incinerator by providing thermal decomposition in atwo-step process. Waste is placed in a chamber which is largely sealedagainst the admission of air except through special openings. Thechamber is commonly refractory lined and may be fitted with auxiliaryburners for use with some types of waste. There is an opening for theadmission of waste, a space for the waste to remain quietly lying on anessentially solid hearth, which has been in turn provided with holessupplying air in limited and, in some cases, controlled quantity. Theair supports enough combustion to release heat which pyrolyticallydecomposes the major portion of the waste. The products arehydrocarbons, carbon monoxide and a very small quantity ofparticulatematerials. These rich gases are ducted to an after burning device inorder to complete the oxidation process. My copending patent applicationfiled concurrently herewith describes an improved device of this type.

In operation, waste is added until the chamber is too full of ash tofunction efficiently or to accept more waste, at which time the processis stopped, the pyrolysis chamber cooled and the residual ash removed bymechanical devices powered or manually operated. The remaining materialis usually a finely divided, light weight, inorganic material mixed withincombustible lumps.

Several weaknesses in the state of the art exist relative to thedecomposition stage, and most center around the configuration andfunction of the hearth and the handling of inert residue. The firstrequirement of the hearth is to support the waste and distribute the airin such a fashion that combustion proceeds uniformly no matter what typethe waste material may be. Items that lay flatly and compactly againstthe bottom or that conform to the shape of the bottom tend to block theholes supplying combustion air and permit inactive areas that may neverburn. Bottom designs employing widely spaced air holes also encouragedead areas. The result of these are the slow or incompletedisintegration of waste and a rapid buildup of residue. The residualmaterials may also be putrescent and unsatisfactory as a fill material.On the other hand, excessively high velocity air directed into the wastematerial may be so great to jet the light ash upward into the gas streamwhere it may remain as a particulate pollutant in the stack gas.

It is highly desirable to be able to operate the pyrolysis chamber forlong periods it is most efficient after it is hot and has developed asmall bed of ash. This is commonly accomplished by building largerchambers or attempting to use ash removal doors during the operation.Large chambers become inefficient and eventually must be cleaned whileopening doors upsets the control of air and produces problems incombustion. Bulk ash removal, either during the burning process or aftershut down, tends to take unburned waste and frequently causes airborneash to be generated either inside or outside the equipment.

SUMMARY OF THE INVENTION It is therefore among the principal objectivesof this invention to provide a hearth structure and associated deviceswhich, when used in a pyrolytic waste destruction chamber, will producemajor improvements in the support of waste of all types, a uniformdistribution of air, velocities sufficiently low to prevent generationof airborne dusts and removal of ash to a location where mechanicalremoval is simplified.

In accord with the objectives, there has now been provided a hearthstructure in combination with a pyrolytic waste destruction chamberwherein the hearth structure comprises at least a pair of oppositelydisposed elongated sloping walls of refractory material which are spacedby and terminate in an elongated openably closed bottom to form atrough-like assembly, a plurality of tubes connected to a pressurizedair supply passing through the sloping walls at longitudinally andtransversely spaced intervals providing air sufficient to maintainproper waste combustion and residue fluidization. Removal of the wasteresidue can be in continuous fashion by employment of an automaticconveyor which removes the same as it is generated or, by gravity orperiodic removal through an exit port provided for that purpose. Thesubject hearth is installed at the bottom of the pyrolysis chamber.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be hereinafter morefully described with reference to the accompanying drawing in which:

FIG. 1 is sectional elevational side view of the invention hearthstructure as positioned at the bottom of the pyrolysis chamber withautomatic conveyor associated therewith and with a suitable after-bumerdevice shown only by phantom lines mounted atop the pyrolysis chamber.FIG. 2 is a sectional front view taken along line 2 2 of FIG. 1 in thedirection of the arrows.

FIGS. 3a and 3b are sectional telescopic views along line 33 of FIG. 2in the direction of the arrows, with two different means of ashresidueremoval shown.

FIG. 3c is a view similar to FIG. 3a and 31) except showing yet anotherembodiment of the invention.

FIG. 4a, 4b and 4c are sectional, fragmented front views of the ashremoval systems of FIGS. 3a, 3b and 3c, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures ofthe drawing and specifically to FIGS. l2, 3a and 4a there is showntherein an essentially closed chamber (e.g. pyrolysis chamber) lined onroof and walls with refractory material 12. The chamber 10 is fittedwith an access door 14 removably fitted over an access port 16 to permitwaste introduction, an exit port 18 for conducting gases generated intoa secondary combustion chamber, such as in my said copending. patentapplication filed concurrently herewith, and a new hearth structure 20which is the subject of the present application.

Hearth structure 20 comprises at least a pair of oppositely disposedelongated sloping planar walls 22 which are sloped at an angle betweenabout 20and 60from the horizontal. The sloping walls 22 terminate in andare spaced by either an openable bottom wall 24 (FIGS. 3b and 412) or bya fixed plate 26 along which the ash may be propelled (FIGS. 3a and 4a.

As shown, particularly in FIGS 1 and 3a, removal of residual ash can beaccomplished by a conventional conveyor (e.g. drag chain or screw)moving through opposing slots 27 located at either end of the fixedplate 26, so that continuous removal may be effected. Or as shown inFIG. 3b, removal can be through bottom gates 32, or by hoe or scoop (notshown) through end door 34.

In another embodiment illustrated by FIGS. 30 and 4c, the hearthstructure is provided with a pair of oppositely disposed spaced slopingplanar walls 36, which are sloped at an angle between about 20 and 60;the same as walls 22, but are at right angles to the latter. Walls 22and 36 terminate in an opening 38 shaped like that formed by an invertedtruncated pyramid. While the embodiment in FIGS. 3b and 4b shows bothbottom opening clean out or end opening clean out access to theincinerated waste in the trough 40, the embodiment shown in FIGS. 30 and4c is provided with a hopper bottom hearth 42 with pivotable sectorgates 44 for ash drop.

In actual practice, only one type of hearth structure would be employed.The hearth walls 22, 36 are made of an abrasion resistant concreterefractory material. The walls 22 and 36 are provided with air ducts 46.These are connected to the refractory surface with air tubes 48connected to a central conventional pressurized air supply 50 onlypartially shown. The tubes are longitudinally and transversely spacedalong the refractory walls and deliver low velocity air to locationsapproximately 6 inches apart, but no more than 9 inches,

when viewed as in FIG. 1. The air blower (not shown) supplies airthrough conduits 51 at velocities of from 1 to 20 feet per second and inan amount sufficient to maintain the combustion rate required bytemperature sensors (not shown) in the stack. This air quantity andvelocity are sufficient to fluidize or move the pulverent ash remainingfrom final combustion. This fluidization is essential since theashnormally has a high angle to repose unless disturbed, with the aid ofthe air blast, the residue moves down the sloping walls to rest at thebottom of the hearth where no air is being introduced. Larger mattersuch as glass and heavy cans no longer supported by the ash fall to thebottom as well.

As earlier mentioned the removal of residual ash (not shown) may be bydrag chain conveyor or screw conveyor (FIGS. 1, 2, 3a and 4) or byremoval through bottom gates or by hoe or scoop through an end door)(FIG. 312), or finally through a bottom dump (FIG. 40).

The steeply sloping hearth walls afford tumbling of boxed waste andpiled papers to permit easier access of combustion supporting air andheat. This is important, especially during start up, when no combustionhas been established. These deep valleys, as it were with air jetsreaching near the top permit much ash storage before the air supply isreduced due to deep coverage of all air ducts.

What is claimed is:

l. A hearth structure in combination with a pyrolytic waste combustionchamber wherein the hearth structure comprises at least a pair ofoppositely disposed elongated sloping walls comprising refractorymaterial which are spaced by and terminate in an elongated openablyclosed bottom to form a resulting troughshaped assembly, a plurality oftubes connected to a controlled pressurized air supply through saidsloping walls at longitudinally and transversely spaced intervalsproviding air sufficient to maintain proper waste combustion andfluidization of resulting combusted ash residue, and wherein anotherpair of similarly oppositely disposed elongated sloping walls areprovided by at right angles to the original said pair of oppositelydisposed walls.

2. A hearth structure according to claim 1 wherein all of saidoppositely disposed walls terminate in an form an openable bottomhearth.

3. A hearth structure according to claim 1 wherein said similarlyoppositely disposed walls are each inclined at an angle between about200 and 4. A hearth structure according to claim 1 wherein all saidsloping walls are inclined at an angle between about 20 and 60.

1. A hearth structure in combination with a pyrolytic waste combustionchamber wherein the hearth structure comprises at least a pair ofoppositely disposed elongated sloping walls comprising refractorymaterial which are spaced by and terminate in an elongated openablyclosed bottom to form a resulting trough-shaped assembly, a plurality oftubes connected to a controlled pressurized air supply through saidsloping walls at longitudinally and transversely spaced intervalsproviding air sufficient to maintain proper waste combustion andfluidization of resulting combusted ash residue, and wherein anotherpair of similarly oppositely disposed elongated sloping walls areprovided by at right angles to the original said pair of oppositelydisposed walls.
 2. A hearth structure according to claim 1 wherein allof said oppositely disposed walls terminate in an form an openablebottom hearth.
 3. A hearth structure according to claim 1 wherein saidsimilarly oppositely disposed walls are each inclined at an anglebetween about 20*0 and 60*.
 4. A hearth structure according to claim 1wherein all said sloping walls are inclined at an angle between about20* and 60*.